Study On Biomechanics Of Bilateral Condyles In Three Surgery Methods Of The Lateral Temporomandibular Joint Ankylosis By Three-dimensional Finite Element Method

Objective:Through establishing the mandible three-dimensional finite elementmodels on which are based to develop three surgery models fortemporomandibular joint ankylosis and analyzing the stress distributionon bilateral condyles of each model with the same load to compare thebiomechanics effect on the bilateral condyles of surged and unsurgedsides with different surgery methods.MethodsA set of CT scan images of a mandible section from a normalgrow-up male are applied to establish a normal mandiblethree-dimensional finite element model. The model is established withimages processed by a finite element soft ware called MSC.Patran in thecomputer based on the principle of three-dimensional finite element griddivision. Then, the right side of the mandible are selected to be the side oftemporomandibular joint ankylosis. And three surgery models areestablished for surface-surface contact temporomandibular jointreconstruction, point-surface contact temporomandibular jointreconstruction and temporomandibular joint arthroplasty. Applying100N of load to the first molars of the bilateral mandible, the condylesstress distribution of the models are analyzed and the stress of surged and unsurged sides of the models are compared. The data are analyzedstatistically by rank transformation nonparametric test.Results:1. Three-dimensional finite element models of normal mandible andthree surgery methods of temporomandibular joint ankylosis have beendeveloped.2. It is found that the Von Mises stress between the bilateralcondyles of normal mandible to have a significant difference (P＜0.05).The stress of right condyle is greater than the left. The Von Mises stressdistribution bilateral condyles trends to have no big difference and thestress increases from condyle transverse ridge to anterior slant surfaceand posterior slant surface.3. The Von Mises stress between the right condyle of thesurface-surface contact temporomandibular joint reconstruction modeland the right normal condyle is found to have no significant difference(P＞0.05). And the Von Mises stress between the left condyle of thesurface-surface contact temporomandibular joint reconstruction modeland the left normal condyle is found to have no significant difference(P＞0.05).4. The Von Mises stress between the right condyle of thepoint-surface contact temporomandibular joint reconstruction model andthe right normal condyle is found to have a significant difference (P＜0.05). The previor is greater than the latter. And the Von Mises stressbetween the left condyle of the point-surface contact temporomandibularjoint reconstruction model and the left normal condyle is found to haveno significant differenc (P＞0.05).5. The Von Mises stress between the fight condyle oftemporomandibular joint arthroplasty model and the fight normal condyleis found to have a significant difference. The previor is less than the latter.And the Von Mises stress between the left condyle of temporomandibularjoint arthroplasty model and the left normal condyle is found to have asignificant difference. The previor is greater than the latter (P＜0.05).Conclusions:1. In this experiment, three-dimensional finite element models havebeen established of a normal mandible and further more, models oftemporomandibular joint ankylosis for three surgery methods have beendeveloped. The models represent the exactly the geometry of themandible and they are more similar to the real mandible.2. In this experiment, the Von Mises stress of both sides of thenormal mandible condyle is found to distribute asymmetrically in themodel.3. When a similar load is applied to the first molars of the bilateralsides of the mandible, the Von Mises stress of the right condyle of thesurface-surface contact temporomandibular joint reconstruction model is similar to the right normal condyle. And the stress of the left condyle ofthe surface-surface contact temporomandibular joint reconstruction modelis similar to the left normal condyle, too. The Von Mises stress of theright condyle of the point-surface contact temporomandibular jointreconstruction model is greater than the right normal condyle. And thestress of the left condyle of the point-surface contact temporomandibularjoint reconstruction model is similar to the left normal condyle. But TheVon Mises stress of the right condyle of temporomandibular jointarthroplasty model is less than the fight normal condyle. And the stress ofthe left condyle of temporomandibular joint arthroplasty model is greaterthan the left normal condyle.4. It is found that temporomandibular joint arthroplasty does notform a condyle similar to the normal mandible joint, and is notconductive to recover chewing functions. It is possible to significantlyincrease the stress of non-surged side of condyle and is unfavorable forthe healthy of temporomandibular joint. It is the worst surgery methodamong the three methods. And the surface-surface contacttemporomandibular joint reconstruction can maximumly resumptionchewing functions. It is the best surgery method among the threemethods.